Instead of wiping out a third of the European populace during the 14th century, suppose the Black Plague had killed 99 out of 100 inhabitants. How would the rest of the world have been affected? What would have happened to Buddhism and Islam with Christianity reduced to a historical footnote?

Kim Stanley Robinson, author of "Antarctica" and the Nebula and Hugo award- winning "Mars Trilogy," excels at both alternate history and large-scale world building, so this premise gives him plenty of material to play with. His new novel, "The Years of Rice and Salt," covers many years and much geographical ground, from the steppes of Mongolia to the western shore of South America, from an alchemist's shop in the Samarqand of the 1700s to the Keltic Sultanate in the 1950s, where the secrets of nuclear fission are about to be uncovered.

The novel begins by recounting the adventures of Mongol horseman Bold Bardash, after he escapes a death sentence from his warlord. Taken as a slave, he befriends a young African boy, Kyu, who is brutally castrated and later becomes an influential eunuch in the Chinese imperial court. The man's and the boy's fate are intertwined, and when one runs afoul of palace politics, the other pays a similarly deadly price.

Because the novel spans a half dozen centuries, Robinson doesn't allow physical death to be the final answer to the earthly conflicts he chronicles. Characters meet in the "bardo," the staging area between life and death. "That was the place souls were sorted out, reconciled to reality, sent back down into the world. Judgment rendered, karma assessed; souls sent back to try again, or released to nirvana." The characters ponder what they've learned, before moving on to their next incarnation. Souls return to the land of the living having traded social classes, genders, nationalities and even biological species.

Bold, Kyu and the supporting cast desperately try to understand why they must struggle so hard without seeming to make any progress. That overarching conflict lends the novel a thematic unity that offsets its episodic structure. Keep an eye out for characters whose names begin with the letters B or K.

"The Years of Rice and Salt" is a timely book, especially in its discussion of the various strains of Islam. Islam is depicted not as some monolithic system of belief, but as open to a wide variety of interpretations and misinterpretations. Robinson treats every culture with respect, never stooping to stereotypes and careful not to imply that all the world's problems could have been solved if only the Caucasian Europeans had been taken out of the picture.

The choices Robinson makes for how his fictional time line diverges from our own seem logical and well thought-out. Because they have been taught crude vaccination techniques, the native North Americans stand a better chance against colonists arriving from both the western and eastern shores. There seems to be no avoiding a world war, but this time the major combatants are the Chinese and the Muslims. The secrets of the atom cannot remain undiscovered forever, but perhaps scientists can control their dissemination before they wind up in the hands of politicians.

Only occasionally does Robinson's sense of historical irony threaten to overwhelm the story. The long episode in which a disgraced alchemist and an inventive glassblower recapitulate the discoveries of everyone from Newton and Copernicus to Galileo and Gutenberg is clever and amusing, but it stretches the reader's credulity before arriving at a heartrending conclusion.

A utopian at heart, Robinson displays an impressively deep understanding of science and philosophy. He isn't interested in spoon-feeding exposition to his readers, so "The Years of Rice and Salt" is not a particularly easy read. But it definitely is a rewarding one, especially if the reader brings to it a reasonable grasp of Asian and Middle Eastern history and religion.

Robinson could well be considered the James Michener of alternate history. He's a subtler, more nuanced writer than the author of "Hawaii," but he knows how to build a compelling story from the clash of cultures, ideas and environments. Like "Antarctica," "The Years of Rice and Salt" has the kind of historical breadth and thematic depth that can attract a wider readership than normal for a work of science fiction.